When a current is applied to the winding of a magnetic bearing, the magnetic field generated forms a loop between the iron core and the thrust plate, forming electromagnetic force between the iron core and the thrust plate; the air gap distance between the revolving shaft and the stator is measured by a displacement sensor, and the electromagnetic force is regulated through adjusting the current in the winding, so as to control the size of the air gap between the revolving shaft and the stator, thereby realizing a stable magnetic suspension.
In the protection system of the magnetic bearing in the prior art, generally, the magnetic bearing bears radial loads, and an auxiliary bearing is provided to radially protect the magnetic bearing when the loads are out of control, but no axial protection for the magnetic bearing is provided. However, the magnetic bearing is applied in the field of centrifugal compressors and mainly bears axial loads.
FIG. 1 is a schematic sectional view of the magnetic bearing in the prior art. As shown in FIG. 1, the magnetic bearing 100 comprises a revolving shaft 110, an iron core 120, a thrust plate 130, and coils 150.
The thrust plate 130 is fixed on the revolving shaft 110, and keeps a distance L from the iron core 120, wherein L>0. When the magnetic bearing is energized, if the control accuracy is not high or the control system is out of control, due to the attraction of the electromagnetic force, the thrust plate 130 approaches to the iron core 120 and finally collides with the iron core 120, and thus the iron core 120 or the thrust plate 130 is damaged.
In view of the defects above, after a long period of research and practice, the inventors finally obtained the present invention.